1. Field of the Invention
The present invention relates to a method of crystallizing an amorphous silicon film or a crystalline silicon film formed on an insulating substrate of glass or the like or promoting crystalline performance thereof by performing laser annealing thereto.
2. Description of Prior Art
In recent years researches have widely been carried out on the technology of crystallizing an amorphous semiconductor film or a crystalline semiconductor film (semiconductor film having crystalline performance constituted not by single crystal but polycrystal, microcrystal or the like), that is, a non single crystal silicon film formed on an insulating substrate of glass or the like or promoting the crystalline performance by performing laser annealing in respect of the film. A silicon film is frequently used for the semiconductor film.
Compared with a quartz substrate which has been frequently used conventionally, a glass substrate has an advantage where the substrate is inexpensive and superior in fabrication performance and a substrate having a large area can easily be formed. Further, laser is preferably used in crystallization process since the melting point of the glass substrate is low. Laser can impart high energy only to a non single crystal film without considerably changing temperature of a substrate.
A crystalline silicon film formed by performing laser annealing is provided with high mobility. Further, researches have been carried out on the technology of forming a thin film transistor (TFT) by using the crystalline silicon film. According to the technology, a liquid crystal electro-optic device of a monolithic type where TFTs for pixel driving and for drive circuit are fabricated on one sheet of a glass substrate, can be provided. The crystalline silicon film is constituted by a number of crystal grains and therefore, the film is referred to generally as a polycrystalline silicon film or a polycrystalline semiconductor film.
Further, a method of performing laser annealing by fabricating a pulse laser beam of an excimer laser or the like having a large output into a square spot of several cm square or a linear shape of several mm widthxc3x97several tens cm on an irradiated face by an optical system and scanning the laser beam (moving an irradiation position of the laser beam relatively in respect of the irradiated face), is preferably used since the method is provided with excellent mass production performance and is industrially excellent.
Particularly, when the linear laser beam is used, high mass production performance can be provided since laser irradiation can be carried out over the entire irradiated face by scanning the laser only in a direction orthogonal to the line direction different from a case of using a laser beam in a spot-like shape where scanning in the forward and rearward direction and in the left and right direction is needed.
Several problems have been posed in performing laser annealing in respect of a non single crystal silicon film by scanning a laser beam of a spot-like shape or a linear shape with a pulse laser beam as a light source.
A particularly serious problem is nonuniformity of effect of laser irradiation in a substrate face. As feature of laser beam, although provision of large energy is pointed out as the most preferable advantage, on the other hand, the pulse laser is provided with a drawback where dispersion of energy for respective shots of pulses is as large as several percent. According to the drawback, when, for example, a liquid crystal display is formed by crystallizing an amorphous silicon film by an excimer laser, there causes an inconvenience where trace of pulse of laser is visualized as it is on picture image.
Such an image failure constitutes a serious drawback in the present age where beautiful picture image is needed. The present invention has been carried out with an object of making inconspicuous or completely eliminating the drawback.
In order to solve the above-described problem, the inventors have paid attention to an atmosphere of a substrate in irradiating laser, performed laser irradiation under various kinds of atmosphere and investigated differences therebetween.
An amorphous silicon film in which the concentration of hydrogen was controlled was selected as an object of laser irradiation. The hydrogen concentration of a film was set to an order of 1020 atoms/cm3. An excimer laser was used for the laser. The result is shown below.
High energy was needed for crystallizing the film when laser irradiation was performed in an atmosphere of a gas having low thermal conductivity such as nitrogen. Meanwhile, when laser irradiation was performed under a state in which a substrate was subjected to an atmosphere of a gas having high thermal conductivity such as hydrogen or helium, a film having high crystalline performance was obtained by comparatively low energy. Further, the temperature of the substrate in laser irradiation was varied in a range of 200xc2x0 C. through 400xc2x0 C. Although comparatively low laser energy was used when the temperature was high, the homogeneity was deteriorated.
The laser irradiation under the atmosphere of the above-described gases only gave rise to a variation in optimum laser energy for crystallization and the homogeneity was not promoted. However, when oxygen was mixed to the atmosphere or only oxygen was used in the atmosphere, the situation was significantly changed. The optimum energy for crystallization was significantly reduced and further, the homogeneity of the film after laser irradiation was also promoted.
It was found from the above-described experiment that oxygen was very effective in promoting the homogeneity and in reducing the optimum laser energy for crystallization. In FIG. 2, an investigation was conducted on the crystalline performance of the substrate in view of half width of Raman half value by varying the atmosphere and the laser energy. The lower the value of the half width of Raman half value, the more excellent is the crystalline performance and therefore, the effect of mixing oxygen is quite apparent. Further, it was found by the above-described experiment that the lower the temperature, the more promoted was the homogeneity. Incidentally, the abscissa designates the energy density (mJ/cm2) and the ordinate designates the half width of Raman half value (cmxe2x88x921).
Oxygen was particularly effective in laser crystallization when the temperature of the substrate was lowered to the room temperature. Under an atmosphere of a gas not including oxygen, at room temperature, enormous laser energy was needed in crystallization by which the productivity was deteriorated significantly. Further, even in the temperature region of 200xc2x0 C. or lower, the lower the temperature, the more improved was the homogeneity. The data is shown in FIG. 4.
FIG. 4 is viewed as follows. According to FIG. 4, the abscissa designates the energy density (mJ/cm2) and the ordinate designates the mean roughness (Ra, nm) in which the state of film roughness is evaluated by an AFM (Atomic Force Microscope) by the laser energy when the atmosphere of the chamber is brought into an atmosphere of the earth, and temperature of the substrate is varied to room temperature, 200xc2x0 C. and 400xc2x0 C. The lower the temperature of the substrate, the higher becomes laser energy necessary for crystallization and therefore, the laser energy is varied such that the crystalline performance having the same degree is obtained at either of the films where the temperature of the substrate is at room temperature, 200xc2x0 C. and 400xc2x0 C. Therefore, the lower the temperature of the substrate, the higher the energy whereby the laser is irradiated.
It is read from the data that the higher the temperature of the substrate, the larger the change in mean roughness of the surface of the film derived from a variation in the laser energy. Accordingly, when a laser having a large amount of variation in the laser energy is used for crystallizing the film, the lower the temperature of the substrate, the more reduced is the in-face dispersion of the mean roughness at the surface of the film. The roughness of the surface of the film has a correlation with the crystalline performance of the film and when the roughness is uniform, the crystalline performance is also uniform.
Photographs clarifying the behavior are prepared in FIGS. 7(A), 7(B) and 7(C). When the film face is roughened by laser irradiation, the film is brightened. The degree of the brightness and the degree of the roughness of the film are correlated with each other and when the degree of the brightness stays the same, the degree of the roughness of the film face also stays the same. FIGS. 7(A), 7(B) and 7(C) are photographs of surfaces when amorphous silicon films are subjected to laser annealing by an excimer laser in which the beam is fabricated in a linear shape. The linear laser is irradiated to the films while scanning from top to bottom direction in the photographs.
In order to search for the optimum energy for crystallization, the laser energy was increased toward the upper direction of the substrate (upper direction in respect of paper face). (Varied by a unit of 5 mJ/cm2) Lengthwise fringes seen in the films are optical interference fringes formed by groups of lenses (refer to FIG. 8) for fabricating the laser beam in a linear shape. When the optical interference fringes are inconspicuous, the homogeneity of crystals is improved.
In FIG. 7(A), a laser processing is performed on the surface of a silicon film at the temperature of substrate of 400xc2x0 C. in an atmospheric environment in a state where the surface of the silicon film is cleaned by an aqueous solution including HF and H2O2 by which the film surface is positively terminated by hydrogen. The laser energy is varied in a range of 255 through 310 mJ/cm2. (The surface energy is varied at intervals of 5 mJ/cm2.)
In FIG. 7(B), the laser processing is performed at room temperature in an atmospheric environment in the same state of the film surface as in FIG. 7(A). The laser energy is varied in a range of 315 through 370 MJ/cM2. (The laser energy is varied at intervals of 5 mJ/cm2.)
In FIG. 7(C), the laser processing is performed at room temperature in an atmospheric environment in a state where an extremely thin natural oxide film is formed on the surface of the silicon film, that is, the surface of the silicon film is not particularly processed. The laser energy is varied in a range of 300 through 355 mJ/cm2. (The laser energy is varied at intervals of 5 mJ/cm2.)
The range of the laser energy differs among the photographs (A), (B) and (C) because the optimum energy for crystallization is varied depending on the state of the film face.
By comparing the photographs (A), (B) and (C), it is found that the photograph (B) is provided with a region of a laser energy for making uniform mostly the brightness of the film surface. (That is, the nonuniformity of film quality is inconsiderable.)
A sixth region from above the photograph (B) corresponds thereto. The film of the photograph (B) is formed by performing laser irradiation at room temperature in an atmospheric environment in the state where the film surface is positively terminated by hydrogen.
A result is obtained in the experiment such that an atmosphere including oxygen is effective in promoting the homogeneity of laser crystallization and the effect is enhanced by positively terminating the surface of the silicon film by hydrogen in the atmosphere and when the temperature of the substrate is selected in the temperature of room temperature through 400xc2x0 C., the room temperature is found to be at optimum.
The thermal conductivity of oxygen is comparatively low among gases and is almost the same as the thermal conductivity of nitrogen. However, why is such a difference caused? The inventors have considered that there must be some chemical change and established the following hypothesis.
The surface of the silicon film before the laser crystallization is generally terminated by hydrogen. Therefore, when the laser crystallization is performed in an atmosphere including oxygen (may be in an atmospheric environment), oxygen reacts with hydrogen on the surface of silicon by the laser energy by which water molecules are formed.
The formed water molecules are distributed on the surface of the substrate in a form of a thin layer in a gaseous state, a liquid state or a state where gas and liquid are coexistent and serve as a heat insulating layer restraining the diffusion rate of heat from the substrate in laser crystallization. When the laser crystallization is performed while heating the substrate, even if a water molecule layer is formed, the layer is swiftly diffused and therefore, the heat insulating effect of the water molecule layer is difficult to cause. Occurrence and extinction of the water molecule layer is repeated along with the laser irradiation.
Assuming that the above-described hypothesis is correct, the inventors have provided intentionally the water molecule layer directly on the silicon film in the laser crystallization and performed the laser crystallization. The method of forming the water molecule layer is as follows.
The surface of silicon is intentionally and positively terminated by hydrogen.
For example, when the upper face of a non single crystal silicon film is cleaned by an aqueous solution including HF, or an aqueous solution including HF and H2O2 before performing the laser crystallization, the rate of termination by hydrogen on the surface of the silicon film is significantly increased. When the above-described hypothesis is correct, the amount of forming water molecules in the laser irradiation is increased by an increase in the amount of hydrogen on the silicon surface and the temperature maintaining effect is promoted. Naturally, in this case, the laser irradiation is performed in an atmosphere including oxygen. The effect of the method has been verified by FIGS. 7(A), 7(B) and 7(C).
Laser crystallization is performed by conducting nitrogen purge added with moisture. Specifically, a portion or all of nitrogen gas is subjected to bubbling in water and is sent to the laser irradiation chamber. When the effect of promoting the homogeneity can be confirmed by this method, the temperature maintaining effect of the water molecule layer can be confirmed.
The laser crystallization is performed by conducting nitrogen purge added with oxygen and hydrogen. The amount of hydrogen has been set to about 0.1% through 10% in consideration of the safety. This method intends to provide water molecules by synthesizing gaseous oxygen and hydrogen by the laser energy.
The second and the third methods have achieved an effect comparable to or more than that in the first method. Therefore, it has been found that provision of the water molecule layer directly above the semiconductor film is effective in promoting the homogeneity of crystal.
In the case where the laser beam fabricated in a linear shape is used as a laser of the laser crystallization, when a gas flow in an air knife shape (hereinafter, referred to as air knife) is formed by the purge gas and the laser irradiation is performed while impinging the gas flow to a portion where the laser is being irradiated, more water molecules are supplied and the effect is promoted. A similar effect is achieved even when the air knife is not made to impinge directly the laser-irradiated portion so far as the air of the air knife is sufficiently supplied to above the portion of the film where the laser is irradiated. However, according to the second and third methods, when the amount of added moisture or the amount of oxygen and hydrogen is excessively large, an adverse effect is resulted.
Generally, a beam having a short wavelength as in an excimer laser does not penetrate a certain depth or more of water and therefore, it is anticipated that when water molecules of the water molecule layer form an aggregation exceeding a certain density, the effect of the laser irradiation is significantly reduced. The adverse effect explains well of the phenomenon.
According to the above-described methods, the in-face homogeneity of the crystalline substrate is significantly promoted by any of them and traces of pulses of the laser are made almost inconspicuous. A particularly excellent point of the methods resides in that grain sizes of crystals are distributed around a range of 2000 xc3x85 through 3000 xc3x85. The dispersion of sizes of the grain sizes of the crystals is as small as xc2x120% or smaller in "sgr" (Standard Deviation) FIGS. 9(A) and 9(B) show photographs visualizing the behavior.
FIG. 9(A) is an SEM photograph (Scanning Electrode Microscope photograph) of the surface of the silicon film in which a substrate where terminations of hydrogen are intentionally provided on the surface of an amorphous silicon film is subjected to laser irradiation at room temperature (RT) in an atmospheric environment.
FIG. 9(B) is an SEM photograph of the surface of a film subjected to laser irradiation with conditions the same as those in FIG. 9(A) except the temperature of the substrate that is set to 400xc2x0 C. According to the film on which the laser irradiation is performed in a state where the temperature of the substrate is as high as 400xc2x0 C., the grain sizes are distributed in a wide range from as large as xcexcm order to as small as several hundreds xc3x85. Meanwhile, in the case of the film on which the laser irradiation is performed where the temperature of the substrate is at room temperature, the grain sizes are provided with a distribution having a peak in a comparatively narrow range of 2000 xc3x85 through 3000 xc3x85. The fact indicates that the grain sizes are distributed uniformly when the laser crystallization is performed under conditions whereby the layer of water molecules formed by the laser irradiation is difficult to diverge.
Further, the dispersion in height of irregularities on the surface of the semiconductor film caused by the laser irradiation becomes smaller than in the conventional case. The fact is indicated by FIG. 4. It is known that the energy of a pulse laser is varied by xc2x15% in the case of an excimer laser. The variation of 5% of the energy density that is actually irradiated corresponds to about 10 through 20 mJ/CM2 in FIG. 4. When the energy density is varied by the width of 10 through 20 mJ/cm2, the mean roughness is varied by xc2x170% or more at the temperature of the substrate of 400xc2x0 C. whereas it is confined to xc2x140% or less when the temperature of the substrate is room temperature. These numerical values coincide substantially with the value of "sgr" calculated by performing a statistical treatment on the irregularities of the substrate.
The present invention disclosed in the specification has been obtained from the above-described experimental result.
According to a first aspect of the present invention, there is provided a method of performing laser annealing by irradiating a laser beam to a non single crystal semiconductor film:
wherein the laser beam is irradiated while forming a temperature holding layer of heat of a gas or a liquid on a side of a face irradiated with the laser beam.
The temperature holding layer helps promote to crystallize the non single crystal semiconductor film by maintaining the temperature of the non single crystal semiconductor film.
The effect of the temperature holding layer is promoted when it comprises water or water vapor. Because water is one of substances having the largest heat capacity in fluids. It is preferable that the temperature holding layer comprises water or water vapor promoting to crystallize the non single crystal semiconductor film.
According to a second aspect of the present invention, there is provided a method of performing laser annealing by irradiating a laser beam to a non single crystal semiconductor film:
wherein the laser beam is irradiated in a state where oxygen and hydrogen are distributed at least at a vicinity of an inside and an outside of a surface of the semiconductor film and oxygen and hydrogen are made to react with each other by the laser beam by which water is formed simultaneously with crystallizing the semiconductor film.
According to a third aspect of the present invention, there is provided a method of performing laser annealing by irradiating a laser beam fabricated in a linear shape to a non single crystal semiconductor film:
wherein the laser beam is irradiated while forming a temperature holding layer of heat of a gas or a liquid on a side of a face irradiated with the laser beam.
The temperature holding layer helps promote to crystallize the non single crystal semiconductor film by maintaining the temperature of the non single crystal semiconductor film.
When the temperature holding layer comprises water or water vapor, the effect is promoted. Because water is one of substances having the largest heat capacity in fluids.
It is preferable that the temperature holding layer comprises water or water vapor promoting to crystallize the non single crystal semiconductor film.
According to a fourth aspect of the present invention, there is provided a method of performing laser annealing by irradiating a laser beam fabricated in a linear shape to a non single crystal semiconductor film:
wherein the laser beam is irradiated in a state where oxygen and hydrogen are distributed at least at a vicinity of an inside and an outside of a surface of the semiconductor film by which oxygen and hydrogen are made to react with each other by the laser beam whereby water is formed simultaneously with crystallizing the semiconductor film.
A pulse laser is effective for the laser used in the first through fourth aspects of the present invention. An excimer laser having a particularly large output in the pulse laser is effective for the laser used in the first through fourth aspects of the present invention.
According to a fifth aspect of the present invention, there is provided a method of performing laser annealing by irradiating a laser beam to a non single crystal semiconductor film:
wherein the laser beam is irradiated to the non single crystal semiconductor film in an atmosphere including at least oxygen and under a state where a surface of the non single crystal semiconductor film is intentionally terminated by hydrogen.
According to a sixth aspect of the present invention, there is provided a method of performing laser annealing by irradiating a laser beam to a non single crystal semiconductor film:
wherein an inside of a laser irradiation chamber capable of controlling an atmosphere thereof is brought into an atmosphere including at least water molecules and the laser beam is irradiated to the non single crystal semiconductor film in the laser irradiation chamber.
According to a seventh aspect of the present invention, there is provided a method of performing laser annealing by irradiating a laser beam to a non single crystal semiconductor film;
wherein the laser beam is irradiated to the non single crystal semiconductor film in a laser irradiation chamber in a state where an inside of the laser irradiation chamber capable of controlling an atmosphere thereof is brought into an atmosphere including at least oxygen and hydrogen by which oxygen and hydrogen are made to react with each other by the laser beam and water is formed simultaneously with crystallizing the semiconductor film.
When the above-described non single crystal semiconductor film is brought into a state where the surface of the non single crystal semiconductor film is intentionally terminated by hydrogen before the laser irradiation, the laser crystallization is carried out further uniformly in the film face. This is because synthesizing of water is performed at a vicinity of the film face, resulting in expediting the temperature maintaining effect.
According to an eighth aspect of the present invention, there is provided a method of performing laser annealing by irradiating a laser beam to a non single crystal semiconductor film:
wherein the laser beam is irradiated to the non single crystal semiconductor film while forming a layer constituted by water molecules in a range from a surface of the non single crystal semiconductor film to just the vicinities of the surface.
According to a ninth aspect of the present invention, there is provided a method of performing laser annealing by irradiating a laser beam to a non single crystal semiconductor film:
wherein the laser beam is irradiated to the non single crystal semiconductor film in a state where a layer constituted by water molecules is formed in a range of from a surface of the non single crystal semiconductor film to just the vicinities of the surface.
In either of the above-described laser annealing processes, when it is carried out in a state where the temperature of the substrate is maintained in a range of xe2x88x9210xc2x0 C. through 100xc2x0 C., the crystalline performance of the film is promoted to be made further uniform.
According to a tenth aspect of the present invention, there is provided a method of performing laser annealing by irradiating a laser beam to a non single crystal semiconductor film:
wherein the laser beam is irradiated to the non single crystal semiconductor film while blowing a gas including water molecules to the non single crystal semiconductor film.
According to an eleventh aspect of the prevent invention, there is provided a method of performing laser annealing by irradiating a laser beam to a non single crystal semiconductor film:
wherein the laser beam is irradiated to the non single crystal semiconductor film while blowing a gas including oxygen and hydrogen to the non single crystal semiconductor film.
In respect of the tenth or the eleventh aspect of the present invention, when laser annealing is carried out in a state where the temperature of the substrate is maintained in a range of xe2x88x9210xc2x0 C. through 100xc2x0 C., the crystalline performance of the film can be promoted to be made further uniform.
The laser annealing process according to the tenth or the eleventh aspect of the present invention, achieves an effect in preventing contamination when the process is carried out in a laser irradiation chamber capable of controlling an atmosphere thereof. Particularly, in respect of the eleventh aspect of the present invention, hydrogen is used and therefore, laser irradiation chamber is needed for safety.
In either of the fifth through the eleventh aspects of the present invention, the irradiation of the laser beam is preferably carried out by scanning a laser beam having a sectional shape of an irradiated face in a spot-like shape or a linear shape. A pulse laser is effective in respect of the laser used in the fifth through the eleventh aspects of the present invention. An excimer laser having particularly large output in the pulse laser is effective for a laser used in the fifth through the eleventh aspects of the present invention.
According to a twelfth aspect of the present invention, there is provided a method of performing laser annealing by irradiating a laser beam which is fabricated in a linear shape to a non single crystal semiconductor film:
wherein a gas flow in an air knife shape is formed by a gas including water molecules and while blowing the gas flow in the air knife shape to the non single crystal semiconductor film, the laser beam is irradiated to a portion of the non single crystal semiconductor film to which the gas flow in the air knife shape is blown.
According to a thirteenth aspect of the present invention, there is provided a method of performing laser annealing by irradiating a laser beam which is fabricated in a linear shape to a non single crystal semiconductor film:
wherein a gas flow in an air knife shape is formed by a gas including oxygen and hydrogen and while blowing the gas flow in the air knife shape to the non single crystal semiconductor film, the laser beam is irradiated to a portion of the non single crystal semiconductor film to which the gas flow in the air knife shape is blown.
The reason of forming the gas flow in the air knife shape in respect of the twelfth and the thirteenth aspects of the present invention, is that the section of the air knife resembles with the beam shape of the linear laser beam and therefore, the gases can be supplied efficiently to a portion where the laser is irradiated. In respect of the twelfth and the thirteenth aspects of the present invention, when the laser annealing is performed in a state where the temperature of the substrate is maintained in a range of xe2x88x9210xc2x0 C. through 100xc2x0 C., the crystalline performance of the film is promoted to be made further uniformly.
In respect of the twelfth and the thirteen aspects of the present invention, when the laser annealing process is carried out in a laser irradiation chamber capable of controlling an atmosphere thereof, an effect is achieved in preventing contamination. Particularly, in the thirteenth aspect of the present invention, hydrogen is used and therefore, the laser irradiation chamber is needed for safety.
A pulse laser is effective for the laser used in the twelfth and the thirteenth aspects of the present invention. An excimer laser having a particularly large output in the pulse laser is effective for the laser used in the twelfth and the thirteenth aspects of the present invention.
A non single crystal silicon film is suitable for the non single crystal semiconductor film used in the first through the thirteenth aspects of the present invention.
According to a fourteenth aspect of the present invention, there is provided a laser annealing device for performing laser annealing to a non single crystal semiconductor film in a laser irradiation chamber capable of controlling an atmosphere thereof, said device comprising:
means for supplying a gas including at least water molecules into the laser irradiation chamber.
According to a fifteenth aspect of the present invention, there is provided a laser annealing device for performing laser annealing to a non single crystal semiconductor film in a laser irradiation chamber capable of controlling an atmosphere thereof, said device comprising:
means for supplying a gas including at least hydrogen an d oxygen into the laser irradiation chamber.
According to a sixteenth aspect of the present invention, there is provided a laser annealing device for performing laser annealing to a non single crystal semiconductor film, said device comprising:
means for supplying a gas including at least water molecules to a portion of the non single crystal semiconductor film to which a laser beam formed by the laser annealing device is irradiated.
According to a seventeenth aspect of the present invention, there is provided a laser annealing device for performing laser annealing to a non single crystal semiconductor film, said device comprising:
means for supplying a gas including at least hydrogen and oxygen to a portion of the non single crystal semiconductor film to which a laser beam formed by the laser annealing device is irradiated.
According to an eighteenth aspect of the present invention, there is provided a laser annealing device for forming a laser beam which is fabricated in a linear shape for performing laser annealing to a non single crystal semiconductor film, said device comprising:
means for forming a gas flow in an air knife shape by a gas including at least water molecules; and
means for supplying the gas forming the gas flow in the air knife shape to a portion of the non single crystal semiconductor film to which the laser beam formed by the laser annealing device is irradiated.
According to a nineteenth aspect of the present invention, there is provided a laser annealing device for forming a laser beam which is fabricated in a linear shape for performing laser annealing to a non single crystal semiconductor film, said device comprising:
means for forming a gas flow in an air knife shape by a gas including at least hydrogen and oxygen; and
means for supplying the gas forming the gas flow in the air knife shape to a portion of the non single crystal semiconductor film to which the laser beam formed by the laser annealing device is irradiated.
A pulse laser is suitable for a laser of the fourteenth through the nineteen aspects of the present invention. An excimer laser having a particularly large output in the pulse laser is suitable for the laser of the eighteenth and the nineteenth aspects of the present invention. A non single crystal silicon film is suitable for the non single crystal semiconductor film used in the fourteenth through the nineteenth aspects of the present invention.
In either of the above-described aspects of the present invention, nitrogen gas is suitable as other component of the above-described gases in view of cost, low reactivity and the like.
According to the present invention, in crystallizing or promoting crystalline performance of a non single crystal semiconductor film by performing laser annealing on the film, a layer of water molecules is formed between the non single crystal semiconductor film and a laser beam. A layer of water molecules operates the non single crystal semiconductor film as a temperature holding layer and significantly promotes homogeneity of the crystalline performance in a film face.
As mentioned above, the effect of the layer of water molecules is varied significantly by the density of the water molecules. This is because a beam having a short wavelength does not penetrate water in a liquid state by a certain depth or more. A laser beam is provided with a short wavelength since it is an ultraviolet ray.